The present invention concerns the improved preparation of pyridinyloxyphenol compounds by reaction of a 2(6)- or 4-substituted pyridine intermediate with a hydroquinone reactant in the presence of an excess amount of a base. The invention also concerns the conversion of bis(pyridinyloxy)benzene compounds to the desired pyridyloxyphenol compounds by similar treatment with a hydroquinone and excess base.
The reaction of 2(6)-substituted pyridine compounds with a hydroquinone and an alkaline material to form correspondng substituted pyridinyloxyphenol compounds (hereinafter collectively referred to for convenience as "POP" compounds), useful as herbicides, is disclosed in abstracts of Japanese Patent Application Nos. SHO-50-29556 and SHO-49-118676, and by U.S. Pat. No. 4,046,553 issued Sept. 6, 1977, which is based on both said patent applications.
However, it has now been discovered that the direct use of a hydroquinone reactant suffers from disadvantages in that significant amounts, e.g., as much as 25-50% or more of the expected desired product yield, of undesired bis(pyridinyloxy)benzene compounds (hereinafter collectively referred to as "bis by-products") are formed, thus detrimentally affecting product yield and quality as well as manufacturing economics. The formation of one such by-product (I) with the desired product (II) is illustrated by the following reaction sequence: ##STR1##
Accordingly, it is an object of the present invention to provide an improved method for producing pyridinyloxyphenol compounds without the significant production of undesired bis by-products.
It is also an object of the present invention to provide a novel method for the conversion of undesired "bis by-products" to the desired pyridinyloxyphenol derivatives, when treated alone or in the context of recycling in the production of the desired POP derivatives starting with 2(6)- or 4-substituted pyridine and hydroquinone.